Issue #2937889 by larowlan, Sam152: Regression: LinkWidget no longer supports base fields with optional title

core/modules/link/src/Plugin/Field/FieldWidget/LinkWidget.php

@@ -227,7 +227,7 @@ class LinkWidget extends WidgetBase {
 
       if (!$element['title']['#required']) {
         // Make title required on the front-end when URI filled-in.
-        $field_name = $this->fieldDefinition->get('field_name');
+        $field_name = $this->fieldDefinition->getName();
 
         $parents = $element['#field_parents'];
         $parents[] = $field_name;

core/modules/link/tests/modules/link_test_base_field/link_test_base_field.info.yml

@@ -0,0 +1,8 @@
+name: Link test base field
+description: Tests link field as an optional base field
+type: module
+core: 8.x
+hidden: true
+dependencies:
+  - link
+  - entity_test

core/modules/link/tests/modules/link_test_base_field/link_test_base_field.module

@@ -0,0 +1,35 @@
+<?php
+
+/**
+ * @file
+ * Contains main module functions.
+ */
+
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Field\BaseFieldDefinition;
+use Drupal\Core\Field\FieldStorageDefinitionInterface;
+use Drupal\link\LinkItemInterface;
+
+/**
+ * Implements hook_entity_base_field_info().
+ */
+function link_test_base_field_entity_base_field_info(EntityTypeInterface $entity_type) {
+  $fields = [];
+  if ($entity_type->id() === 'entity_test') {
+    $fields['links'] = BaseFieldDefinition::create('link')
+      ->setLabel(t('Links'))
+      ->setRevisionable(TRUE)
+      ->setCardinality(FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED)
+      ->setDescription(t('Add links to the entity.'))
+      ->setRequired(FALSE)
+      ->setSettings([
+        'link_type' => LinkItemInterface::LINK_GENERIC,
+        'title' => DRUPAL_REQUIRED,
+      ])
+      ->setDisplayOptions('form', [
+        'type' => 'link_default',
+        'weight' => 49,
+      ]);
+  }
+  return $fields;
+}

core/modules/link/tests/src/Functional/LinkFieldTest.php

@@ -24,7 +24,12 @@ class LinkFieldTest extends BrowserTestBase {
    *
    * @var array
    */
-  public static $modules = ['entity_test', 'link', 'node'];
+  public static $modules = [
+    'entity_test',
+    'link',
+    'node',
+    'link_test_base_field',
+  ];
 
   /**
    * A field to use in this test class.